The effect of human factors on the helmet-mounted display.
--Gen William "Billy" Mitchell
IN WORLD WAR I, the mounting of machine guns on airplanes marked the official beginning of the evolution of pilot-centered weapons employment. The technological advancement of combat aircraft and pilot-to-vehicle interface has enjoyed steady growth throughout the history of these aircraft. Following the innovation of the mounted machine gun, the development of both airborne radar and the infrared search-and-track system allowed fighter pilots to cue their weapons beyond the bore line of the airplane.
In most fighter aircraft, the field of view of these two cueing systems is approximately plus or minus 60 degrees off the aircraft's bore line. Although both systems are very important to one's ability to use weapons beyond visual range, the employment of heat-seeking missiles and modern machine guns still requires the pilot to point the nose of the fighter jet at the target. Consequently, fighters can find themselves engaged in long-turning fights, thus becoming vulnerable to both the aircraft with which they are engaged as well as other enemy aircraft in the area--a deadly scenario.
Introduction of the head-up display (HUD) marked the first step toward allowing pilots to cue their missiles or guns with an out-of-the-cockpit aiming device. A giant leap forward in terms of pilot-to-aircraft interface, the HUD displayed not only accurate weapons-aiming symbols, but also relevant flight data such as airspeed, altitude, and heading (fig. 1). For the first time, pilots could view such information without looking back inside the cockpit.
[FIGURE 1 OMITTED]
Currently, the development of high off-boresight weapons is driving the latest work in pilot-centered weapons employment. Many foreign air forces already have this capability, and a number of others are acquiring it. Dean F. Kocian of the Air Force Research Laboratory's Human Effectiveness Directorate addresses the evolution of high off-boresight weapons and their dramatic impact on fighter aircraft:
Since the mounting of machine guns on airplanes in World War I, pilots have pointed the nose of their aircraft in the direction of the target. The dynamics of airborne combat required pilots to outmaneuver each other. Superior aircraft speed and agility were the keys to a successful engagement; however, that scenario has changed.... This scenario represents a total paradigm shift in the way air-to-air combat is fought. The sighting reference for cueing a weapon is no longer the nose of the aircraft, but rather the pilot's helmet. As long as the target is within visual range and the pilot can view the target through the display in the helmet visor, the relative position of the aircraft to the enemy is not critical, but tactical implications are profound. (1)
In order to cue high off-boresight weapons to the target in a visual dogfight, pilots must have a helmet-mounted aiming device, which itself represents a human-factors breakthrough. Since the beginning of aerial combat, air forces around the world have run a technological race aimed at gaining superiority through increased propulsion and maneuverability of fighter aircraft. But these new levels of performance can take a toll on humans. For example, pilots subjected to high-G forces risk loss of consciousness and extended incapacitation; however, the helmet-mounted target cue and high off-boresight weapons enable the missile, capable of more than 50 Gs, to execute the high-G turn instead of the pilot.
Development of the Helmet-Mounted Display
The United States Air Force has worked on a helmet-mounted display for fighter aircraft for roughly 30 years. The proliferation of various types of high off-boresight weapons by enemy countries lends a sense of urgency to fielding this capability as soon as possible. Indeed, the fact that the Air Force is not holding on to the leading edge of this technology places our combat capability in the visual environment at risk. Less proficient pilots flying inferior aircraft enjoy a distinct advantage because they have a helmet-mounted display system.
The Russian MiG-29 Fulcrum and its AA-11 Archer high off-boresight, heat-seeking, short-range missile are considered the primary threat in the visual environment. MiG-29 pilots acquired helmet-mounted cueing devices for use almost a decade ago. Even though they are rudimentary, using only a flip-down aiming monocle and lacking missile-cueing symbols, they give the Russians a tremendous advantage in visual dogfighting. Ironically, the Israeli air force, which purchases its F-15 and F-16 fighter jets from the United States, also outpaces us in this arena because it has fielded a display and sight helmet (DASH) for those aircraft.
Essentially, helmet-mounted displays are "must have" equipment on fourth-generation fighter aircraft since high off-boresight weapons and visual cueing outweigh any aircraft-performance advantage in dogfighting. For that reason, the Air Force and Navy are currently in the process of acquiring and fielding the Joint Helmet-Mounted Cueing System (JHMCS), the most advanced such system in the world (fig. 2), which--together with the AIM-9X high off-boresight, short-range, heat-seeking missile--will soon allow the United States to regain the advantage in aerial combat.
[FIGURE 2 OMITTED]
Vista Sabre II, the JHMCS's initial prototype, provided a building block for helmet-display development. Several helmet-mounted trackers and displays had emerged parallel to the Vista Sabre program, but significant performance or safety problems limited their utility. In conjunction with the 422d Test and Evaluation Squadron at Nellis AFB, Nevada, Vista Sabre II performed the initial operational-utility evaluation, beginning in 1993. Kaiser Electronics produced the electronic components and helmet hardware, while McDonnell Douglas's software engineers developed the operational flight program for the F-15's computer, which would allow the helmet-mounted displays to function and interface with aircraft-weapons information.
The evaluation uncovered several important human-factor or "liveware"-to-hardware issues related to helmet cueing and the employment of off-boresight weapons. The first concerned the problem of poor helmet fit and its effect on helmet-display performance. Although the new helmet-mounted display hardware was incredibly light, the center of gravity and increase in relative weight under nine-G loads tended to shift the helmet on the pilot's head during high-G maneuvering. Because a magnetic field in the cockpit of the aircraft senses the position of the helmet and feeds the current line of sight from the helmet to the aircraft's flight computer, any such shifting would generate errors, thus making the accurate pointing of the missile seeker at a target nearly impossible. Specifically, the Vista Sabre II test found that static pointing errors of more than two degrees could render aiming capability ineffective.
The evaluation also noted the inability of pilots to hold their heads steady during high-G turns and aircraft buffeting, the latter designating the shaking sensation one feels when the aircraft performs at the edge of the flight envelope during a high angle of attack. Vista Sabre II revealed that the system needed interface suppression to smooth head bounce during high-G maneuvers and in regions of aircraft buffeting. Otherwise, the pilot's ability to aim with the helmet is severely degraded.
Furthermore, in a finding referred to as "eyeball critical sensor," pilots expressed concern over reflections and glare associated with the helmet display. Early visors had a noticeable "patch" that enhanced contrast and created a more discernable display--vital to sustaining good vision and, therefore, flight safety. Clearly, the Vista Sabre II program proved most effective in establishing a starting point for the evolution of helmet-mounted displays.
The Visually Coupled Acquisition and Targeting System (VCATS), the follow-on system to Vista Sabre II, made its inaugural flight in February 1997, successfully bridging the gap from the prototype helmets of the earlier program to today's JHMCS helmets. The VCATS targeted problems revealed by Vista Sabre II's operational utility evaluation. For example, it implemented the custom of equipping helmets with space-age gel liners and ear cups in order to achieve the fit required for optimum cueing performance. Moreover, the VCATS helmet visors were custom ground to fit precisely around the mask and lock into place, creating more stability and helping eliminate glare from under the visor, while tracker algorithms and more precise system integration nearly eliminated static pointing errors discovered in early helmet tests. The VCATS also implemented high-update-rate trackers, accelerometers, and digital-filter algorithms for active noise cancellation, vastly improving head bounce under high-G loads and aircraft buffeting. In order to combat the eyeball-critical-sensor issues, the VCATS removed the visor patch and utilized "hot-tube" cathode-ray-tube technology to reduce glare and increase contrast in the visor display. In general, the VCATS system successfully overcame the problems revealed by the early Vista Sabre II test.
In addition to taking on problem areas unearthed by Vista Sabre II, the VCATS also integrated the helmet-cueing capability into the "hands on throttle and stick" (HOTAS) functions of the F-15--a compatibility critical to the pilot-centered interface with the helmet system. The system also ensured full compatibility with night operations; indeed, fighters throughout the world may soon see displays--typically projected on the helmet visor--in the field of view of their night vision goggles (NVG). In the case of the VCATS, testing has proven the compatibility with panoramic NVG (fig. 3).
[FIGURE 3 OMITTED]
The VCATS program proved itself invaluable to the development of the JHMCS and the advancement of helmet-mounted displays in the US military. According to Kocian,
an outstanding example of human-centered design, VCATS advances the [Air Force's Human Effectiveness Directorate] mission to maximize the potential of Air Force warfighting personnel. The directorate's primary goal is to link, via human-system integration, technological advances in controls, displays, and information-handling with the military pilot's human factors including sensory, perceptual, cognitive, and motor capabilities; strength and anthropometrics; experience; and skills. (2)
Human Factors in Helmet-Cueing Integration
Despite the impressive track record of the VCATS, designers must face several human-factor issues prior to successfully fielding and employing the JHMCS. They must always concern themselves with maximizing the capability of the weapons available and ensuring the safety of the new helmet--especially during the ejection procedure.
First, early helmets did not take into account how often pilots use peripheral vision during a close-range dogfight. In general, while wearing helmets, they can turn their heads approximately 60 degrees from side to side of the aircraft's bore line. New technologies, however, confer upon fourth-generation missiles an off-boresight capability exceeding 60 degrees. In order to compensate for pilots' limited range of head movement, the JHMCS utilizes an "up-look" aiming reference (fig. 4). That is, two up-look reticles provide higher off-boresight cueing capability by allowing pilots to cue the missile with their peripheral vision. Thus, they can utilize the full capability of missile technology and successfully employ weapons beyond 60 degrees off boresight.
[FIGURE 4 OMITTED]
Second, the extra weight of the hardware in a helmet-mounted cueing display might present problems. Although engineers can make the units incredibly light, the operational environment for fighter aircraft is much more complex than the one G experienced here on Earth. Today's fighter pilots attempt to perform high off-boresight helmet cueing under loads up to nine Gs--nine times the force of gravity. But G effects are expediential rather than linear in nature. Since dogfighting pilots constantly move their heads to clear the flight path and maneuver to kill the adversary, having to endure extra weight with a slightly different center of gravity places a tremendous amount of force on their necks. This is a serious concern according to contributors to a panel discussion held at the Aerospace Medical Association Annual Scientific Meeting in Detroit in May 1999, who mention how air forces around the world already lose a considerable number of workdays due to soft-tissue neck injuries. They conclude that these numbers will dramatically jump as more pilots begin to fly with helmet-mounted devices. (3)
Third, in addition to increases in neck injuries due to flying maneuvers, one must also consider the effect of additional helmet weight on the pilot during ejection, particularly the possibility of neck injury due to inertial loading with drogue and parachute deployment. Other problems could arise from an increase in helmet size and inattention to windblast. (4) Engineers and developers must balance capability against pilot safety, perhaps opting to decrease the maximum limits of maneuver aircraft if the pilot is equipped with a helmet-cueing system.
Finally, flying with JHMCS increases the potential for spatial disorientation as well as task saturation. Most fighter pilots are used to flying with HUD information, which is always in the same place relative to the airplane--on the bore line in the direction the aircraft is traveling. But flying with "HUD-like" displays on the visor can initially be disorienting because information is now located wherever they happen to be looking at the time. The problem is compounded at night due to the general lack of either a horizon or visual cues. Furthermore, having to keep up with aircraft parameters such as altitude, heading, and airspeed displayed directly in front of the right eye while attempting to employ and monitor weapons during dogfighting can quickly become overwhelming to pilots. To help lessen the danger of helmet displays contributing to this sort of task saturation, designers have enabled a HOTAS function so that pilots can blank the display if it becomes distracting in the tactical environment. Obviously, human-factor issues concerning helmet-mounted cueing systems should not be taken lightly. Awareness of these issues, along with proper education and training, can help prevent such problems from leading to tragedy.
Potential of Helmet Development
Helmet-mounted displays have evolved at a rapid pace over the last decade, and the future may hold even more technological advances for military helmets. Short-term improvement projects include voice commands and sound-direction recognition; long-range technological advancements might include imagery transmission and piloting by remote virtual helmets and cockpits.
The integration of sound into the next generation of pilot helmets seems inevitable, with several companies already developing and testing the use of voice commands. In fact, Robert K. Ackerman notes that voice commands will eventually take the place of HOTAS measures to provide rapid response to the demands of air combat. (5) Future pilots may also have the luxury of flying with a three-dimensional sound system within their helmet, currently under development for use in the French-built Rafale fighter. The system will provide direction-specific cues that alert pilots to the direction of the threat and that distinguish between different types of threats by means of various sounds. (6) Future US helmets for pilots of Joint Strike Fighters will feature night vision, sound, and other sensors.
Although the next giant leap in helmet technology might seem far away, one finds growing interest in pilots flying unmanned aerial vehicles (UAV) by wearing a helmet in a virtual cockpit and receiving images, just as they would if they were actually in the aircraft. Technological developments could overcome obstacles involving photo imagery, data transmission, and display, thereby enabling the rapid growth of UAVs.
Human factors and pilot-centered design in aviation have a long and colorful history, beginning with the mounting of machine guns on aircraft and progressing through advanced weapons displays on helmet visors. By recently conquering several technological problems, developers and engineers have enabled helmet-mounted display systems to become a viable and almost necessary part of fighter aircraft. The high off-boresight capabilities of today's fourth-generation missiles, along with the challenge of overcoming human limitations, are partly responsible for the growth of helmet-mounted cueing devices. We have also seen that this innovative system carries with it certain risks, such as spatial disorientation, task saturation, and ejection compatibility, that engineers and users must address. But the advantages of helmet-mounted displays and the possibility of adding refinements like sound integration and virtual control hold great promise for the future of this technology.
(1.) Dean F. Kocian, "Human-Centered Design Project Revolutionizes Day and Night Air Combat," no. HE-00-10 (Wright-Patterson AFB, OH: Air Force Research Laboratory, Human Effectiveness Directorate, 2001), http://www.afrlhorizons.com/Briefs/June01/HE0010.html (accessed August 13, 2003).
(3.) "Military Flight Helmets: Is Head Protection Still Important?" (panel discussion chaired by Lt Col R. Munson at the Aerospace Medical Association Annual Scientific Meeting, Detroit, May 1999), http://www.geocities.com/iamfsp/panel.htm (accessed September 19, 2003).
(5.) Robert K. Ackerman, "French Helmet Visors Clear the Skies for Combat Pilots," Signal Magazine, August 1996, http://www.us.net/signal/Archive/Aug96/French-aug.html (accessed August 13, 2003).
MAJ JAMES R. VOGEL, USAF
DR. MARIAN C. SCHULTZ
DR. JAMES T. SCHULTZ *
* Maj James R. Vogel is an F-15 instructor pilot currently assigned to the 85th Test and Evaluation Squadron at Eglin AFB, Florida. He has been selected as part of the initial cadre for the F/A-22 and will be reassigned to Nellis AFB, Nevada. Dr. Marian C. Schultz, a tenured associate professor of management and management information systems at the University of West Florida, has served as a consultant for numerous organizations. Dr. James T. Schultz, a tenured associate professor of aviation business administration at Embry-Riddle Aeronautical University, is currently the program chair for the bachelor of science program in management of technical operations at Embry-Riddle.
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|Author:||Vogel, James R.; Schultz, Marian C.; Schultz, James T.|
|Publication:||Air & Space Power Journal|
|Date:||Mar 22, 2004|
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